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Chapter 12 · The Balm of the Trees - Terpenes
12
citronellal, nerol, geraniol or citronellol. Citronellal is an important starting material for the
synthesis of isopulegol and menthol. Citral is also
condensed with acetone to pseudoionone in basic
media, which is then cyclized to β-ionone in an
acidic medium. Because of their violet-like odor,
ionones are frequently used as fragrance components.
Some important monocyclic monoterpenes
are presented in . Fig. 12.5. The terpenes shown
here are all derived from the para-menthane skeleton, i.e. from 1-methyl-4-isopropyl-cyclohexane.
Limonene, often also referred to as “dipentene”,
occurs particularly frequently in nature, e.g. in
orange and mandarin oils. In this group, in addition to hydrocarbons, there are also numerous
alcohols, such as (−)-menthol, which smells of
peppermint. In . Fig. 12.5 (+)-carvone, which
5 The two enantiomeric citronellols are
light yellow oils which differ in smell:
(R)-citronellol occurs in the citronella oils
of lemongrass, the (S)-enantiomer smells of
geranium oil.
In the group of acyclic monoterpene aldehydes,
the cis/trans isomers geranial and neral are of
importance. Both together are also called citral.
In the literature also the names citral A (= geranial) and citral B (= neral) can be found. Citral
is the main component of lemongrass oil, but
can also be produced synthetically from isobutene and formaldehyde. Since it is available
in relatively large quantities (2600 t a −1 ), citral
is the starting compound for numerous secondary compounds (◉ . Fig. 12.4). Hydrogenation
of C=C- and/or C=O-double bond(s) produces
OH
OH
OH
OH
O
O
O
O
-Myrcene
-Myrcene
(Z)- -Ocimene
(Z)- -Ocimene
Linalool
Geraniol (E)
Nerol (Z)
(R)-Citronellol
Geranial (E)
Neral (Z)
( R)-Citronellal
(E)-Tagetone
"Citral"
. Fig. 12.3 Important examples of acyclic monoterpenes
Chapter 12 · The Balm of the Trees - Terpenes
12
citronellal, nerol, geraniol or citronellol. Citronellal is an important starting material for the
synthesis of isopulegol and menthol. Citral is also
condensed with acetone to pseudoionone in basic
media, which is then cyclized to β-ionone in an
acidic medium. Because of their violet-like odor,
ionones are frequently used as fragrance components.
Some important monocyclic monoterpenes
are presented in . Fig. 12.5. The terpenes shown
here are all derived from the para-menthane skeleton, i.e. from 1-methyl-4-isopropyl-cyclohexane.
Limonene, often also referred to as “dipentene”,
occurs particularly frequently in nature, e.g. in
orange and mandarin oils. In this group, in addition to hydrocarbons, there are also numerous
alcohols, such as (−)-menthol, which smells of
peppermint. In . Fig. 12.5 (+)-carvone, which
5 The two enantiomeric citronellols are
light yellow oils which differ in smell:
(R)-citronellol occurs in the citronella oils
of lemongrass, the (S)-enantiomer smells of
geranium oil.
In the group of acyclic monoterpene aldehydes,
the cis/trans isomers geranial and neral are of
importance. Both together are also called citral.
In the literature also the names citral A (= geranial) and citral B (= neral) can be found. Citral
is the main component of lemongrass oil, but
can also be produced synthetically from isobutene and formaldehyde. Since it is available
in relatively large quantities (2600 t a −1 ), citral
is the starting compound for numerous secondary compounds (◉ . Fig. 12.4). Hydrogenation
of C=C- and/or C=O-double bond(s) produces
OH
OH
OH
OH
O
O
O
O
-Myrcene
-Myrcene
(Z)- -Ocimene
(Z)- -Ocimene
Linalool
Geraniol (E)
Nerol (Z)
(R)-Citronellol
Geranial (E)
Neral (Z)
( R)-Citronellal
(E)-Tagetone
"Citral"
. Fig. 12.3 Important examples of acyclic monoterpenes